Ion traps reactions

The rate constant of the ion-trapping reaction, kz, is much larger than the propagation rate constant, at least in cyclic ether and acetal polymerizations. The ratio kz [pRii/yw] is large and termination is instantaneous compared with growth [136], In this way, the number of centres can be determined at any moment during polymerization. The chemical shifts of some quaternary phosphonium ions (of structure corresponding to terminated polyheterocyclic chains) are summarized in Table 2. 

Pitteri, S.J. Chrisman, P.A. Hogan, J.M. McLuckey, S.A. Electron transfer ion/ion reactions in a three-dimensional quadrupole ion trap Reactions of doubly and triply protonated peptides with SOj". Ana/. Chem. 2005, 77, 1831-1839. 

FIGURE 2.3 Representativemassspectrafortheieactionofdeprotonated2-deoxy-5-cytidine monophosphate (5-dCMP) with D2O in a quadrupole-ion trap. Reaction times are (a) 0 ms, (b) 250 ms, (c) 2000 ms, and (d) 10,000 ms. Peaks are labeled as D , where n equals the number of incorporated denterinm atoms. (Reproduced from Chipuk, J.E. Brodbelt, J.S. J. Am. Soc. Mass Spectrom. 2007,18, 724-736. With permission from Elsevier.)... 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

Collision-induced dissociation mass spectrum of tire proton-bound dimer of isopropanol [(CH2)2CHOH]2H. The mJz 121 ions were first isolated in the trap, followed by resonant excitation of their trajectories to produce CID. Fragment ions include water loss mJz 103), loss of isopropanol mJz 61) and loss of 42 anui mJz 79). (b) Ion-molecule reactions in an ion trap. In this example the mJz 103 ion was first isolated and then resonantly excited in the trap. Endothennic reaction with water inside the trap produces the proton-bound cluster at mJz 121, while CID produces the fragment with mJz 61. 

The same procedure as outlined above can be used to study ion-molecule reactions [15, 34]- Mass-selected ions will react with neutral species inside the trap. The presence of the damping gas means that stable (tliemiodynamic and... 

As with the quadmpole ion trap, ions with a particular m/z ratio can be selected and stored in tlie FT-ICR cell by the resonant ejection of all other ions. Once isolated, the ions can be stored for variable periods of time (even hours) and allowed to react with neutral reagents that are introduced into the trapping cell. In this maimer, the products of bi-molecular reactions can be monitored and, if done as a fiinction of trapping time, it is possible to derive rate constants for the reactions [47]. Collision-induced dissociation can also be perfomied in the FT-ICR cell by tlie isolation and subsequent excitation of the cyclotron frequency of the ions. The extra translational kinetic energy of the ion packet results in energetic collisions between the ions and background... 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

However, a maximum is reached at about 15 volts, and a decrease is observed at higher voltages. With increasing voltage, the kinetic energy of the primary ions is also increased. The increase in primary ion current apparently is counterbalanced and finally exceeded by the decrease in the cross-section of the ion molecule reaction. In addition, discrimination of CH5 + ions which are formed via a complex becomes more effective. At a potential of 20 volts between trap and chamber, most of the primary ions have kinetic energies around 20 e.v., and a secondary CH5+ ion... 

The reactions of the gold anion Au- and of the di- and triatomic gold cluster monoanions Au2- and Au3- with CO were studied in a radio-frequency octopole ion trap experiment at cryogenic temperatures. Au- shows no affinity for CO, but the two cluster anions absorb up to two CO molecules. Particular stability has been ascribed to [Au3(CO)2]-, for which the binding energy has been estimated from thermolysis rate coefficients.292... 

Various analyzers have been used to analyze phenolic compounds. The choice of the MS analyzer is influenced by the main objective of the study. The triple quadrupole (QqQ) has been used to quantify, applying multiple reaction monitoring experiments, whereas the ion trap has been used for both identification and structure elucidation of phenolic compounds. Moreover, time-of-flight (TOF) and Fourier-transform ion cyclotron resonance (FT-ICR) are mainly recommended for studies focused on obtaining accurate mass measurements with errors below 5 ppm and sub-ppm errors, respectively (Werner and others 2008). Nowadays, hybrid equipment also exists, including different ionization sources with different analyzers, for instance electrospray or atmospheric pressure chemical ionization with triple quadrupole and time-of-flight (Waridel and others 2001). 

The quadrupole ion trap traps ions in an electric field generally in the presence of a buffer gas (He). The theory and some of its uses have been discussed by March (26). Ion molecule reactions in ion traps have been reviewed (27). The quadrupole ion trap is a relatively new instrument commercialized <20 years ago and the new generation of instruments has only been available since 1995. Thus gas-phase inorganic chemistry using a quadrupole ion trap is as yet relatively hard to find, but on the increase. 

The FT-ICR/MS is an ideal instrument for studying ion-molecule reactions over an extended time scale due to the excellent trapping of ions in the cell and the unmatched mass resolution and mass accuracy. Mass resolution is defined as the mass divided by the peak width at half height... 

Quadrupole ion trap mass spectrometers may trap ions for longer times and allow reactions up to 10 s. 

Where reactions are to be studied, specific ions may be selected using a quadrupole or a magnetic sector and the ions passed through a reaction cell containing the reactant gas, generally diluted with an inert gas. With ion traps, all the ions enter the cell and are mass selected and reacted with the reagent gas. 

Some experiments (Table 1, Experiments No. 97 and 108) were carried out in one leg of an H-shaped reactor. After the killing of the reaction, all volatiles were distilled into the other leg of the reactor which was then scaled off, and its contents were analysed by GLC for ethanol. We hoped to measure in this way the ethanol formed from the sec-oxonium ions by reaction (v), but as the results show, the recovery of ethanol was rather incomplete, presumably because much of it remained trapped in the polymer. In some experiments a phial containing a measured amount of water was broken before the initiator phial (Table 1, Experiments No. 115, 111 B, 114). 

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